An analog-digital converter operating on the basis of the sigma-delta principle is described, by way of example, in Sansen, W.; Huijsing, J. H.; Plassche, R. J. van de: “Analog Circuit Design, Mixed A/D Circuit Design, Sensor Interface Circuits and Communication Circuits”, Kluwer Academic Publishers, page 175. This converter comprises a first converter stage which is supplied with an analog input signal which is to be converted and with a first feedback signal, a second converter stage which is supplied with an output signal from the first converter stage and with a second feedback signal, and a comparator stage which is supplied with an output signal from the second converter stage. The comparator stage has an output stage connected downstream of it which has a digital integrator which produces a digital multibit signal as output signal from the converter. To feed back this multibit output signal to the first converter stage, a one-bit digital-analog converter (D/A converter) is provided which converts the multibit signal into a single-bit signal and which is operated at a higher clock frequency in comparison with the comparator stage. A further D/A converter converts the multibit output signal into the second feedback signal supplied to the second converter stage.
Mödl, S. et al. “14 bit ΣΔ modulator with multibit feedback”, Proceedings of the 22nd European Solid-State Circuits Conference pp. 224–227, 1996, Neuchatel, Switzerland, describes an A/D converter having a converter stage which is supplied with an analog input signal which is to be converted and with a pulse-width-modulated feedback signal. The converter stage has a comparator stage connected downstream of it and the comparator stage has a digital integrator connected downstream of it, the integrator providing a multibit signal as output signal. To feed back the output signal to the one converter stage, there is a digital-analog converter (D/A converter) which is supplied with the multibit signal and which produces the pulse-width modulated signal. For these and other reasons there is a need for the present invention.